In a sheet post-processing apparatus, the sheets sent from the image forming apparatus of a photocopier or printer are sequentially stacked on an intermediate stacker, and these sheets are arranged to form a bundle of sheets. The bundle of sheets having been formed is subjected to various forms of post-processes such as stitching by a stapler. This sheet post-processing apparatus has been put into common use over an extensive field.
With an increase in the operation speed of the image forming apparatus, the aforementioned sheet post-processing apparatus is required to enhance the throughput, and several techniques have been proposed.
In the conventional sheet post-processing apparatus, when a process of stitching the sheet bundle mounted on an intermediate stacker is finished, several sheets of paper are placed sequentially from the top sheet on the intermediate stacker in order to form a bundle of sheets for the next process of stitching.
One proposal for increasing speed is as follows. While a process of stitching is applied to the bundle of sheets placed on the intermediate stacker, two leading sheets out of the sheets for forming a bundle of sheets to be subjected to the next stitching operation are placed one on top of another on the sheet conveyance path located immediately before the intermediate stacker. Upon completion of the process of stitching the preceding bundle of sheets the sheets are fed out to the intermediate stacker. This is intended to reduce the overall time of forming the bundle of sheets (e.g., Unexamined Japanese Patent Application Publications No. H5-254704 and No. H9-235069).
However, even when the sheets are waiting on the sheet conveyance path, some of the conveying rollers arranged on the sheets conveyance path rotate in contact with the sheets. This may cause the waiting sheets to be scratched or contaminated.